1. Introduction
This invention relates to electroless metal plating and more particularly to a means for increasing the plating rate of an electroless nickel plating solution.
2. Description of the Prior Art
Electroless metal deposition refers to the chemical plating of a metal over an active surface by chemical reduction in the absence of an external electric current. Processes and compositions useful therefore are known, are in substantial commercial use, and are described in numerous publications. For example, compositions for depositing electroless nickel are described in U.S. Pat. Nos. 2,690,401; 2,690,402; 2,762,723; 2,935,424; 2,929,742; 3,338,726; 3,420,680 and 3,515,564, all incorporated herein by reference.
Known electroless nickel deposition solutions generally comprise at least four ingredients dissolved in a solvent, typically water. They are (1) a source of nickel ions, (2) a reducing agent for the nickel ions such as a hypophosphite, (3) an acid or hydroxide pH adjustor to provide required pH, and (4) a complexing agent for the nickel ions sufficient to prevent precipitation in solution. A large number of suitable complexing agents for electroless nickel solutions are described in the aforesaid U.S. Patents. In some formulations, a complexing agent is helpful but not a necessity.
In addition to the basic additives comprising the electroless nickel solution as described above, other additives are routinely added to such solutions in minor amount. These additives comprise, for example, stabilizers to prevent spontaneous decomposition of the solution, brightners to improve deposit appearance exaltants to improve plating rate and the like.
Though plating solutions of the type described have been brought to a high level of development, considerable efforts are still made to further improve such solutions.